The retina is the light-sensitive layer of tissue that lines the inside of the eye and sends visual messages through the optic nerve to the brain. The center of the retina is called the macula and is the only part capable of fine detailed vision.
Due to several causes such as cataract surgery, posterior vitreous detachment, diabetic proliferative retinopathy or trauma, the retina can become separated from its underlying layer of support tissues. When the retina detaches, it is lifted or pulled from its normal position and is removed from its blood supply and source of nutrition.
Initial detachment may be localized, but if untreated, the entire retina may become detached. The retina will degenerate and loose its ability to function if it remains detached. Central vision will be lost if the macula remains detached. If not appropriately treated, retinal detachment may thus cause permanent vision loss and lead to blindness.
The causes of retinal detachment can be divided into three main categories: (1) Rhegmatogenous retinal detachment, due to a retinal break or tear which allows the vitreous liquid to pass through the break and lift off the retina (2) exudative retinal detachment, due to leakage of fluid from under the retina and (3) traction retinal detachments: This type of detachment is due to pulling on the retina usually from fibro-vascular tissue within the vitreous cavity; proliferative diabetic retinopathy and proliferative vitreoretinopathy (scar tissue developing in association wit a rhegmatogenous retinal detachment) are the most common causes of tractional retinal detachment.
Vitrectomy is a surgical procedure consisting of the mechanical removal of vitreous liquid by the mechanical cutting and aspiration of the vitreous humour through a surgical instrument called a vitrector.
Vitrectomy may be used in the following clinical situations: (1) retinal detachment (2) complications or bleeding from diabetic eye disease (3) clouding of the vitreous jelly from one of many causes including blood, inflammatory debris or infection (4) macular hole (5) epiretinal membrane (6) a foreign body which has entered or passed through the eye and (7) intraocular infections (endophthalmitis).
Vitrectomy followed by injection of a retinal tamponade is a common technique used to repair retinal detachments. Retinal tamponade is achieved by either air, gas or silicone oil. Air and gas are temporary tamponades that last anywhere from days (air) to weeks depending upon the type of gas used (typically SF6 or C3F8). Silicone oil is used to achieve a permanent tamponade until the oil is surgically removed. The choice of tamponade is determined by the pathology, with longer tamponades (C3F8 or silicone oil) employed for more complicated cases such as tractional retinal detachment. Gas resorbs spontaneously based on its physicochemical properties, but silicone oil is removed when and if the retina is felt to be healed and stable. After healing, the oil tamponade is withdrawn by aspiration and replaced by a specific balanced salt solution, which is then replaced by fluid produced by the eye. Silicone oil removal can be tedious, and often is incomplete, with residual oil being unremoved due to small droplets or emulsified oil being caught behind or underneath tissues such as the iris or lens capsule. The residual oil usually causes problems such as persistent floaters or glaucoma (elevated intraocular pressure).
Tamponades may be characterized by two main physico-chemical properties. The first property is the tamponing power; this property is given by a high surface tension of the solution; it allows the liquid to close the breaks in the retina and avoids leaking of the tamponade into the sub-retinal space. The second property is the force of reapplication; this property is given by a high difference of density between the tamponade and the vitreous fluid; this property is used to restore the retina to its initial place and to move the sub-retinal fluid out of the sub-retinal space created by the detachment.
The use of intraocular gases (usually either perfluoropropane (C3F8) or sulfur hexafluoride (SF6) or air) may be useful for flattening a detached retina or tamponading a macular hole and allowing an adhesion to form between the retina and its supporting tissues. These tissues need to be in apposition for a period of time, typically days to weeks, for this to occur. It is frequently necessary to maintain a certain head position following surgery when gas is used (see Macular Hole page). Vision in a gas filled eye is usually rather poor until at least 50% of the gas is absorbed. Possible complications of intraocular gas include progression of cataracts and elevated eye pressure (glaucoma). It is unsafe to fly in a plane or travel to high altitude while gas remains in the eye. The gas resorbs prior to adequate healing, and repeated injections are necessary.
The use of silicone oil is occasionally necessary instead of gas to keep the retina attached postoperatively. Different silicone oils may be used. Some of these oils have a density of below 1 to treat the retinal detachment of the upper part of the retina and some oils have a high density for treating the detachment of the lower part. Their surface tension is not very high but they have densities that provide a good force of reapplication. However, silicone oils may emulsify in the vitreous cavity resulting in a haze in the visual field. Also, when withdrawn, there are always small droplets that remain in the vitreous cavity inducing long term toxicity and visual problems due to the bubbles. If some silicone oil passes in the anterior chamber, it can lead to a difficulty to treat glaucoma. Inflammations of the posterior segment can be observed with these oils. Silicone remains in the eye until it is removed (necessitating a second surgery at a later date). Like gas, silicone oil can promote cataracts, cause glaucoma, and may damage the cornea. Silicone oil may lead to inflammation, which may participate to reproliferation of scar tissue (proliferative vitreoretinopathy) and recurrent tractional detachment. Furthermore, retinal detachment and vitrectomy can be associated with other conditions such as inflammation, proliferative symptoms, infections etc. The tamponade actually used are not associated with active substances able to treat or prevent these conditions.
To avoid these drawbacks, several attempts have been made.
A polymer gel has been developed (WO 99/21512) as tamponade. This is a photodymanic polymer which will gel when exposed to light and push back the retina. However, there is concern regarding toxicity issues due to the photodynamic ingredients of this gel.
WO 2006/078458 describes the use of a hydrogel of hyaluronic acid made with deuterium water. In this patent application, tamponade with increased density, in comparison to water, by addition of deuterium water and hyaluronic acid is attempted.
A recent patent (WO 2009/037384) uses a plastic bag placed in the vitreous cavity to be filled with the silicone oils. This strategy should avoid remaining oil after withdrawal. However, this procedure necessitates a second surgery to withdraw the bag at the end of the treatment.